Pretreatment of rats (and other rodents) with isoniazed or hydrazine results in an increased rate of defluorination of the general anesthetic enflurane by liver microsomes. Analysis of liver microsomes by SDS gel electroporesis or DE-52 anion exchange chromatography did not reveal any differences in either the amount or type of cytochrome P-450) caused by treatment with either compound. Analysis of microsomal lipids indicates that there are no apparent differences between lipids extracted from the microsomes of control rats and those from pretreated animals. However, analysis by DE-53 anion exchange chromatography suggests the presence of a "new" minor band of cytochrome p-450 in the microsomes obtained from the livers of rats treated with hydrazine. These results indicate that a new form of cytochrome P-450 might be responsible for the increased rate of metabolism of enflurane to the potential kidney toxin F. Whether or not other hydrazine containing drugs such as hydralazine, carbidopa, procarbazine, and phenylbutazone induce a similar form of cytochrome P-450 remains to be determined.